<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    *{
        margin: 0;
        padding: 0;
    }
    .table{
        width: 500px;
        height: 100px;
        margin: 20px;
        display: table;
    }
    .table-row{
        display: table-row;
        
    }
    .table-cell{
        display: table-cell;
        vertical-align: center;
        border: 2px solid black;
    }
    .left{
        background: red;
        opacity: 0.3;
    }
    .right{
        background: blue;
    }
</style>
<body>
    <div class="table">
        <div class="table-row">
            <div class="left table-cell">left</div>
            <div class="right table-cell">right</div>
        </div>
    </div>
</body>
</html>